There have been known various room temperature vulcanizable silicon rubber compositions that turn into rubbery elastic bodies at room temperature. Vulcanized rubbers obtained from room temperature vulcanizable silicone rubber compositions (abbreviated as RTV silicone rubber compositions hereinafter) are superior to other organic rubbers in weatherability, durability, heat resistance, and cold resistance, and hence they find use in various fields, particularly building construction, as an adhesive for glass to glass or glass to metal or as a sealant for concrete joints. It has recently come into general use as a coating material for buildings, plants, and water pipes (both inside and outside).
Unfortunately, the RTV silicone rubber composition is composed mainly of organopolysiloxane which easily becomes charged and attracts dust in the atmosphere. Therefore, the sealing or coating material based on it becomes markedly stained with time after curing, which deteriorates its good appearance. One way proposed so far to address this problem is by incorporation of RTV silicone rubber composition with a surface active agent having polyoxyethylene groups, sorbitan residues, disaccharide residues, or the like (JP-A 56-76452 and JP-A 56-76453). For this method to be effective, a large amount of surface active agent is necessary, and this deteriorates the adhesiveness which is important for RTV silicone rubber composition as a sealing or coating material.
Underwater structures and ships are vulnerable to attack by aquatic organisms sticking to or growing on their submerged parts. Such aquatic organisms living in sea and river include barnacle, ascidian, serpula, moule, mussel, Bugula neritina, green seaweed, and sea lettuce. They increase the frictional drag of ships, which leads to reduced speed and increased fuel consumption to maintain the constant speed, and it is disadvantageous for cost. Also, they deteriorate the performance of underwater structures or they even eat the base material. They also clog set nets or culture nets to kill fish.
One conventional way to protect underwater structures from attack by aquatic organisms was by their coating with an antifouling paint containing a poisonous antifouling agent such as organotin compound or cuprous oxide. It almost completely prevents aquatic organisms from sticking to or growing on underwater structures but it is not desirable from the standpoint of environment, safety, and hygiene at the time of its production and coating on account of the poisonous antifouling agent it contains. Moreover, the poisonous antifouling agent gradually dissolves from the coating film in water and eventually causes water pollution after a long period of time. Thus, antifouling paints have come to be banned.
In the meanwhile, there has been proposed a nontoxic paint composed of an RTV silicone rubber composition and liquid paraffin or petrolatum, which is free of poisonous antifouling agents and yet effective in preventing aquatic organics from sticking to or growing on underwater structures (JP-A 58-13673 and JP-A 62-84166). There has also been proposed a nontoxic antifouling paint composition which is composed of a reaction-curable silicone resin and a polar group-containing silicone resin. It produces its effect in such a way that the first component shrinks as curing proceeds, thereby allowing the second component (which is incompatible and non-reactive with the first one) to bleed out from it. In addition, the first component has a low surface tension which enhances the antifouling effect (Japanese Patent Nos. 2503986 and 2952375). Unfortunately, the foregoing nontoxic antifouling paint composition poses problems with environment, safety, and hygiene because the second component is a silicone resin which has polyoxyalkylene groups (adducts of ethylene oxide with propylene oxide) connecting to Si atoms through C—C bonds or a silicone resin having alkoxyl groups connecting to terminal Si atoms through ethylene oxide groups or propylene oxide groups.
In addition, there has been proposed a curable composition which contains organopolysiloxane (having condensation reactive functional groups at both ends of molecule) and hydrophobic silica (JP-A 2001-139816). There has also been proposed a curable composition which contains organopolysiloxane (having condensation reactive functional groups at both ends of molecule), hydrophobic silica, and hydrophilic silica (JP-A 2001-181509). These compositions are comparatively good in thixotropic properties, so that they give a thick coating film on a vertical plain by a single coating process. However, they are highly viscous and poor in sprayability. Upon dilution with a solvent, they rapidly lose their thixotropic properties and easily cause sagging, which leads to coating film poor in smoothness.
There is also proposed a blend of two kinds of silicone rubber differing in viscosity which gives a thick coating film even though it is diluted with a solvent (JP-A 10-316933). However, this blend is incorporated with only hydrophobic silica and hence does not possess low viscosity, high strength, and high thixotropic properties all at once. In addition, it does not give a smooth coating film with a glossy surface.
It is known that the thixotropic properties (or non-sagging properties) of high-viscosity materials can be greatly improved by incorporation with a non-sagging agent (such as polyether) and a proper filler. The main filler in use for general-purpose silicone sealing materials which are currently available on the market includes treated silica of dry process and colloidal calcium carbonate with surface treatment. Silica of dry process is used in combination with polyether having a molecular weight of 300 to 200,000 as a non-sagging agent (U.S. Pat. No. 4,261,758 and JP-B 2-48586). There is disclosed a combination of dry process silica (whose surface is pretreated with octamethylcyclotetrasiloxane) and a polysiloxane-polyether copolymer linked with a carboxyl group (JP-A 1-245057). There is disclosed a combination of polyether (having hydrolyzable silyl groups at both ends) and a filler (JP-A 61-21158). There is disclosed a combination of polypropylene glycol (having ketoxime groups at both ends) and fumed silica (JP-A 62-135560). There is disclosed a combination of specific silicone (modified with polyoxypropylene) and wet process silica (JP-A 2006-342327). These compositions are intended to impart non-sagging properties to high-viscosity materials, and their disclosures suggest nothing about making highly thixotropic the sprayable low-viscosity materials as proposed in the present invention.